I think that's backwards. Google without Search has very little to most of the Internet, and Google knows it. Search is the basis of Google's Ad money, and they won't do anything to restrict that.
Other search engines are good enough to work if a user's unhappy, and Google hopes that users never have a reason to notice that.
If Google can do what Amazon is doing with product searches in a "one click" purchase model the trade will pay off in forcing people to sign in. A huge huge portion of Google income is from direct purchases, which is why Amazon is arguably its biggest competitor, not Bing. At the very least searches are much less relevant if you aren't signed in, and that gap is only going to continue to grow imo.
Other search engines are good enough to work if a user's unhappy, and Google hopes that users never have a reason to notice that.